The invention relates to an improved polymer membrane or thin film used in chemical technology. More particularly, the invention relates to a triaxially oriented polymer membrane produced by the rolltrusion process.
Polymers, by definition, are long chain molecules in which the atoms are bound to one another by means of strong covalent bonds. Hence one would expect exceptionally high strength and stiffness values in the chain direction since the applied load would then be opposed by the covalent bond themselves. On the contrary, most of the commercial polymers exhibit strength and stiffness values far below their theoretical limits. It is established that the modulus values of most of the commercial polymers are at least an order of magnitude less than their theoretical limits, thus severely limiting their use in many structural or load bearing applications. One of the many ways to improve engineering properties lies in the preparation of highly chain extended/oriented polymers. Another is to create a well regulated non-spherulitic morphology with oriented crystalline regions separated by amorphous regions which may be oriented to varying degrees to create a workpiece with improved properties in 3-D (three directions). The latter approach is unique and forms the basis for rolltrusion, a new process, and its applications. This rolltrusion process is discussed in the above parent case, U.S. Ser. No. 275,707, filed Nov. 22, 1988. It is not simply the crystallinity of the polymer that determines its properties but the morphological distribution of crystalline and amorphous regions and their respective sizes and states of orientation. As engineering materials polymers offer several advantages over metals and ceramics, in terms of high strength to weight ratio, cost efficiency, easy processability and improved corrosion resistance in many applications. See Table 1.
The need for oriented polymers has led to the development of several orientation techniques such as solid state deformation of polymers, preparation of polymers with rigid chemical structures; and crystallization/fiber spinning from gels and dilute solutions. Much of the research in oriented polymers during the past two decades have been devoted towards an improvement and understanding of processing-morphology property relations in uniaxially oriented systems. However, in the present invention, we are concerned with the preparation of highly triaxially oriented polymers from commercial plastics produced by the rolltrusion process, which produces a membrane for use in chemical technology.